Database
[{email:"email@example.com",password:"password_hash",info:{birthday:"1993-03-12"}}]
Query
db.collection.aggregate([{$set:{birthday:{$dateFromString:{dateString:"$info.birthday",format:"%Y-%m-%d"}}}},{$set:{age:{$subtract:[{$subtract:[{$year:"$$NOW"},{$year:"$birthday"}]},{$cond:[{$lt:[{$dayOfYear:"$birthday"},{$dayOfYear:"$$NOW"}]},0,1]}]}}}])